<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
  <style>
    .foo {
      color: red;
    }
  </style>
</head>

<body>
  <div id="root"></div>
  <script type="text/babel">
    class Clock extends React.Component {
      constructor(props) {
        super(props)
        this.state = { date: new Date(), str: navigator.userAgent.toLocaleLowerCase() };
      }
      render() {
        return (
          <div>
            <h1>Hello, world!</h1>
            <h2>现在是{this.state.date.toLocaleTimeString()}</h2>
            <h3>{this.state.str}</h3>

          </div>
        );
      }

    }

    ReactDOM.render(
      <Clock />,
      document.getElementById("root")
    )

  </script>

</body>

</html>